The Process of Heredity 559 



8 About 10 per cent of the embryos are larger and more active 

 than the pure bred individuals, hatch early, some few as early as 

 the earliest of the pure breeds, are darker in color than the latter, 

 have a more efficient circulation, outgrow and outlive the best of 

 the pure strain. 



These last individuals are those in which the blending of charac- 

 ters has produced the most harmonious result. 



We see then that there are all degrees of compatibility of ger- 

 minal material from an entire failure to unite in fertilization to the 

 production of a type of hybrid that is better fitted to cope with its 

 environment than either of the pure strains. 



The Rhythmic Flux of Characters 



Many of the facts brought out by the data presented serve to 

 emphasize the idea of heredity as a process. Instead of a fixity 

 of relationship between pure strains and hybrids, there is a constant 

 flux. At one time we see the paternal influence in the ascendancy, 

 only to be overshadowed later on in development by the maternal 

 influence. If we were to make the statement that in M hybrids 

 the presence of heteroclitus sperm accelerates the process of 

 development, we would be overlooking the fact that this influence 

 is at best transitory, that the acceleration is evident only after 

 about twenty-four hours of development, and that, after a period 

 of from seven to ten days the M pure strain develops more rapidly 

 than the M hybrid. The latter gradually loses its developmental 

 momentum and comes to a complete stop, due probably to its 

 inability to handle a large mass of yolk that remains unassimilated. 



In the case of the H hybrids, too, we would be wrong if we 

 stated unqualifiedly that the introduction of F. majalis sperm 

 retards development. In the first place no measurable retarda- 

 tion is evident until a lapse of about sixteen hours, on the average. 

 In the second place the more successful of the hybrids overtake 

 the average H pures after six or seven days, and although the 

 majority of the hybrids subsequently lose ground, a few maintain 

 their advantage and after hatching outgrow the best of the pure 

 strain. 



There is no fixity of characters here, but everything is flux and 



